1. The Field of the Invention
The present invention relates to novel orthopedic casting materials, and in particular, to orthopedic casting materials which are formulated so as to have improved lamination between adjacent layers of the materials.
2. The Prior Art
Many different orthopedic casting materials have been developed for use in the immobilization of broken or otherwise injured body parts. Some of the first casting materials developed for this purpose involve the use of plaster of Paris bandages.
More recently, polyurethane prepolymers were found to be extremely useful in formulating a resin for orthopedic casting materials, as disclosed, for example, in U.S. Pat. No. 4,502,479 (Garwood et al.), U.S. Pat. No. 4,609,578 (Reed), U.S. Pat. No. 4,667,661 (Scholz et al.), and U.S. Pat. No. 4,774,937 (Scholz et al.). Most commonly, a knitted fiberglass fabric is used as the scrim onto which such polyurethane prepolymers are coated.
In the quest for an improved orthopedic casting material, those skilled in the art recognize that effective layer to layer lamination of the orthopedic casting material upon application and after cure is of the utmost importance. One way to increase the lamination properties of a polyurethane prepolymer based orthopedic casting material would be to increase the proportion of the "soft component" primarily responsible for adhesion (e.g., the polyol) to the "hard component" primarily responsible for rigidity (e.g., the isocyanate) in the formulation of the polyurethane prepolymer. Unfortunately, however, although increasing the relative proportion of the soft component generally does result in better adhesion or lamination, the rigidity or strength of the resultant cast is significantly decreased due to the corresponding decrease in the proportion of the hard component. Thus, a compromise must be made between the relative proportions of hard and soft components employed in the resin so as to provide a balance between the properties of strength and lamination in the formulated casting material.
Another approach to increasing the lamination characteristics of an orthopedic casting material is to increase the amount of resin coated onto or impregnated into the scrim. However, increased resin loading often results in resin migration and/or pooling of the resin during storage. This is undesirable not only from the standpoint of losing the resin from the scrim during significant storage periods, but also, such resin migration results in uneven distribution of the resin on the scrim. Such uneven distribution of the resin can adversely affect the handling properties of the material upon application as well as the uniformity of the finished cured cast with regard to such characteristics as resistance to delamination, porosity, and compression strength, etc. Moreover, increased resin loading often decreases the air porosity of the resultant material, and adequate porosity is an important characteristic of orthopedic casting materials.
From the foregoing, it will be appreciated that what is needed in the art is an improved orthopedic casting material which has enhanced lamination properties without the necessity of changing the resin composition. It would be a further advancement in the art to provide orthopedic casting materials which have such enhanced lamination properties without employing increased amounts of resin in the scrim and without decreasing the porosity of the materials. Such orthopedic casting materials and methods for preparing the same are disclosed and claimed herein.